1. Field of the Invention
The present invention relates to an eccentric oscillating gear device, and a method of assembling a crankshaft in the eccentric oscillating gear device.
2. Description of the Related Art
Heretofore, there has been known an eccentric oscillating gear device disclosed in JP 2001-353684A. The eccentric oscillating gear device disclosed in JP 2001-353684A is designed such that an externally toothed gear is oscillatingly rotated interlockingly with a rotation of an eccentric body provided on a crankshaft, to allow an outer cylinder and a carrier to be relatively rotated with respect to each other. In this gear device, the outer cylinder is fixed to a first member of a robot, and the carrier is adapted to be relatively rotated at a given rotation ratio with respect to the outer cylinder, and fixed to a second member of the robot. This gear device is provided with a positioning pin for setting the carrier to a given orientation with respect to the second member of the robot.
Meanwhile, in an operation of assembling an eccentric oscillating gear device, generally, a crankshaft and an externally toothed gear are assembled to a carrier, and then the carrier is assembled to an outer cylinder. In this case, the crankshaft can be assembled to the carrier without any restriction in terms of an eccentric direction of an eccentric body of the crankshaft. However, depending on the eccentric direction of the assembled crankshaft, a rotational phase difference occurs in torsional rigidity of the gear device. This causes a problem that, in cases where the gear device is disassembled during maintenance or the like and then re-assembled, a phase of the torsional rigidity in a rotation direction is changed from that before the disassembling. Moreover, the gear device is free from restriction in terms of the eccentric direction. Thus, there is another problem that an individual difference in phase of the torsional rigidity in the rotation direction occurs between respective ones of a plurality of the gear devices.